N,N'-tetrathiodimorpholines have found utility in the rubber industry as sulfur donors and vulcanization accelerators. Previous methods to prepare N,N'-tetrathiodimorpholine have included adding sulfur to a solution of morpholine disulfide. The problem with this preparation is that the preparation of morpholine disulfide is expensive and cumbersome. Morpholine disulfide is prepared by the reaction of morpholine and sulfur monochloride in the presence of alkali in an organic solvent. M. C. Throdahl and M. W. Harman, Ind. Eng. Chem., 43, 421 (1951).
Another prior art methodology for the preparation of N,N'-tetrathiodimorpholines involves the use of halopolysulfides and morpholine. This procedure uses the highly toxic and corrosive halopolysulfides, for example, sulfur dichloride and dichloropolysulfides.
U.S. Pat. No. 2,911,405 discloses a process for the preparation of N,N'-tetrathiodimorpholines via insertion of sulfur into N,N'-dithiodimorpholine and Chemical Abstracts 40, 732-9 describes a process wherein morpholine and sulfur are reacted in the presence of lead oxide. None of the prior art discloses or suggests a process for the preparation of N,N'-tetrathiodimorpholine based on the oxidation of a morpholine/sulfur mixture in the presence of iron compounds in combination with zinc compounds such as ZnCl.sub.2 and ZnO.
There is a need in the rubber chemical industry for a new proces that efficiently and economically produces N,N'tetrathiodimorpholines which does not require the use of expensive or dangerous starting materials.